in my humble opinion, CD is a coexisting condition to another diagnosis. Since your difficult child has a bipolar parent, he has a 30% chance of being bipolar (see "The Bipolar Child"). My difficult child's father is bipolar also, and many of the behaviors you are describing are similar to what I experienced.
First, you need to get another diagnosis by a pediatric psychiatrist, not a regular psychiatrist. Behaviors present differently in kids than in adults (again, consult "The Bipolar Child"). I would try to find a nearby university hospital, as most times they are informed of the most recent treatments.
Stimulants made my son more aggressive, violent and destructive, and I think they are doing the same to your difficult child. He may need an atypical psychotic if Depakote doesn't work by itself. This combination has been beneficial for us. But it took two hospitalizations and two psychiatrists to get to the right comvination.
Finally, does your difficult child have an IEP? Since he has an adult aid, I would assume that he does. Part of the IEP is a Behavior Intervention Plan (BIP), to help your difficult child have consistent consequences to his behavior. If he doesn't have it, then ask for it. I would also ask the school for a complete psychological profile as well as any deficits in language processing and writing (many ADHD kids have deficits here). This will help the school get your difficult child the help he needs and give you outside resources as well.
Finally, don't beat the child. Did you know that most prisoners have experienced some sort of child abuse, particularly beatings? Violence only begets violence, and it has to stop with each and every one of us. Instead, come up with a household BIP -- explaining what privileges will be taken away for the first offense, the second, etc. It will take a while for him to "get it", but eventually he will. If the two of you can come up with a plan together, and post it where it can be seen, that will help him buy into it.
Good luck, and keep your chin up. These kids are a lot of work, but we're talking about a LIFE, not something that can be replaced. We have a duty as parents/ guardians to ensure that our kids grow up to be healthy, productive members of society. Our kids just force us to go the extra mile (or two or three).